This invention pertains to a fluidized bed gas-solids contact reactor utilizing a dual-sided contactor unit having integral concentric walls adapted for heat exchange with a liquid therein. It pertains particularly to such a reactor using a capped dualsided concentric riser-downcomer unit containing a liquid and located in a module, and which reactor is principally useful for combusting fluidized particulate fuels such as coal to heat the liquid and generate saturated liquid or steam.
The use of fluidized beds has been recognized as an advantageous way of reacting gases and solids such as for generating heat, for example by use with heat exchanger tubes in boilers for generating pressurized steam from feed water passing in heat exchange relation with hot combustion gases from the fluidized bed of fuel. The fluidized bed utilizes a particulate carbonaceous fuel such as coal, and is fluidized by passing air upwardly through the bed to provide the combustion reaction. Advantages of such fluidized bed combustion systems include increased heat transfer rates, increase in combustion efficiency, and reduction in boiler size.
One known form of a gas-solids contactor is disclosed by U.S. Pat. No. 3,826,783 to Zenz, which discloses a folded transfer line reactor for circulating particulate materials for fluidized catalytic cracking (FCC) units. However, such folded riser-downcomer configurations apparently have not been previously used for fluidized bed combustors for particulate fuels such as coal for generating saturated vapors such as steam. Other types of fluidized bed combustors include U.S. Pat. No. 3,910,235 to Highley which discloses a fluidized bed combustion apparatus utilizing internally circulating beds each surrounded by a heat exchange jacket. Also, U.S. Pat. No. 4,240,377 to Johnson discloses a fluidized bed boiler utilizing circulating solids, and U.S. Pat. No. 4,539,939 to Johnson discloses fluidized bed combustion tubular boiler apparatus for combusting coal with limestone to generate steam.
These known large fluidized bed combustion boiler systems have been found to be undesirably complicated and difficult to control the particulate solids flow, and also are quite expensive. Such disadvantages of the prior art reactors and combustion systems have now been advantageously overcome by the present invention, which provides an improved fluidized bed reactor apparatus and method which utilizes at least one central riser and concentric downcomer unit having dual sided heat exchange configurations and located above a fluidized bed for exchanging heat with a liquid in a reactor module.